Surface enhanced Raman spectroscopic (SERS) probes of neurotransmitter concentrations and dynamics will be developed. The probes will work with several classes of neurotransmitters and will require 10 sec to 3 min instrument time, depending on the sensitivity required. For homogenates and perfusates SERS at 1-2 mm diameter electrodes will be used. Micro-electrode technology will be developed for SERS probes for application to brain slices. It is anticipated that SERS will be applicable to more systems and provide more positive identification than voltammetry and will be faster than liquid chromatography. Dopamine will serve as a model system for development of the techniques. The characteristic phenolic C-O stretch and ring mode will be used for quantification. The mechanism of 19a catecholamine adsorption at a silver electrode will be elucidated, using substituted phenols and catechols and dopamine and norepinephrine agonists of known structure. Rat brain homogenates will be used as test samples. Techniques for measurement of 3- methoxytyramine and dopamine or methanephrine and norepinephrine simultaneously will be developed. Two approaches to brain slice SERS measurements will be investigated. An inverted microscope will be used to illuminate 25 m electrodes through a thin tissue slice. For thicker slices, an optical fiber illumination system will be developed. The SERS instrumentation will be adopted and measurement protocols modified for use in histamine and tele-methyl histamine measurements and in serotonin measurements. Exploratory studies in neuropeptides are planned.